None
Not Applicable
This invention relates in general to the distribution of torque and more particularly to a transfer case for splitting torque so that it can be distributed to two outputs.
Most four wheel automotive vehicles, such as sedans, station wagons and vans, operate with the engine torque delivered to only one set of wheels on such vehicles. In some vehicles that set is the rear wheels, but in most vehicles of current manufacture it is the front wheels. However, some manufacturers now offer all-wheel-drive vehicles, and the typical vehicle of this type operates with the engine torque distributed to all four of its wheelsxe2x80x94all the time. To be sure, many light trucks and sport utility vehicles have four-wheel drive, but in a vehicle of this type only two wheelsxe2x80x94usually the rearxe2x80x94normally propel the vehicle, while the remaining two may be called upon to also propel the vehicle if the need arises. This usually requires the driver to operate a switch or manipulate a lever to engage the wheels that are otherwise disconnected from the engine. In contrast, in an all-wheel-drive vehicle, the engine delivers torque to all four wheels basically all the time; no controls exist for disconnecting one or the other of the two sets of wheels from the engine.
A variety of mechanisms exist for distributing engine torque between the front and rear wheels of all-wheel-drive vehicles. Some rely simply on viscous coupling between the front and rear wheels. Others utilize clutches with a variety of mechanisms for operating the clutches. These mechanisms may have the capacity to vary the torque between the front and rear wheels so as to transfer more torque to wheels having the better traction. Indeed, some of these come equipped with highly sophisticated control systems which sense not only slippage between the front and rear wheels, but other operating conditions such as throttle position, gear lever position and engine speed, as well, all to tailor the torque distribution such that it provides the best traction for the driving conditions.
But the typical clutch has plates which accommodate a slight measure of slippage and are urged together with a greater bias when the primary wheels lose traction and begin to slip. However, the torque transferred through the clutch depends on several variables, including the temperature of the clutch, the relative speed between the plates, as well as the force or pressure with which the clutch plates are compressed against each other. These variables make such clutches difficult to control and indeed require complex electronics to effect control.
The present invention resides in a transfer case through which torque is transferred between an input element and two output elements. The transfer case contains a clutch and a planetary gear set and splits the torque into a direct path and an indirect path, with the indirect path passing through both the clutch and the planetary set.